VIRAL PRODUCTION AND VIRUS CAUSED MORTALITY OF BACTERIA IN THE NORTH SEA

A new approach was used to study viral production and virus caused mortality of bacteria in the North Sea. The bacterial size fraction of the microbial community was concentrated using tangential flow filtration and an aliquot was added to virus-free seawater from the same location. The rationale behind this approach is to reduce viral abundance and by that prevent new infection. Bacterial and viral abundance was determined using epifluorescence microscopy of SYBR Green I stained subsamples from the incubations collected at 4-6 h intervals. Viral abundance generally showed a maximum after 10-15 h. The difference in viral counts between the onset of the experiment and the maximum was used to estimate viral production and virus caused mortality of bacteria. Estimates of phage infected bacteria ranged from 10 to 50 % of the bacterioplankton community assuming a burst size of 30 virus particles released per infected bacterial cell. This indicates that a significant portion of bacterial production is channeled into the dissolved organic carbon pool via viral lysis.